This invention relates to a waste disposal treatment of calcium-containing, organically loaded wastewater by means of an activated sludge process under aeration with almost pure oxygen and/or with an oxygen-containing gas.
Calcium-containing, organically loaded wastewaters are obtained from various processes and in particular, from sugar manufacturing operations. Recently, the sugar industry has adopted activated sludge methods for the purification of such wastewaters, either instead of or in conjunction with the utilization of settling ponds and oxidation ponds. Thus, a wastewater purification process is known, for example, wherein the waste waters produced in the sugar manufacturing plant are circulated via a settling tank; the sludge-transporting water coming from the settling tank is first conducted to a sedimentation tank and an anaerobic tank, and thereafter, to a fermentor with a secondary treatment tank connected downstream thereof. Sludge which has settled in the secondary treatment tank is recycled to the fermentor while purified water withdrawn from the secondary treatment tank can be either returned into the settling tank of the flushing and wash water cycle of the sugar operation, or fed to a drainage ditch. The fermentor can be operated with air or at least with oxygen-enriched air (Reference is made to the periodical "Sugar" 28th year, vol. 10, pp. 527-534, 1975, the contents being incorporated herein).
Unfortunately, the operation of such water treatment plants is not trouble-free. Frequently the activated sludge is uncontrollably degenerated resulting in considerable upset in the degradation efficiency of the secondary treatment. The cause of this phenomenon is primarily due to an unbalanced supply of nutrients, especially when the plants are either underloaded or overloaded. The resulting degenerated sludge, called bulking sludge, can exist, for example, as long threads of bacteria having a low settling velocity. When such a bulking sludge condition occurs, there is a marked slowdown in the separation in the secondary treatment tank into the activated sludge, which is returned into the aeration plant, and into the clear stream discharged into the drainage ditch.
Moreover, a reduction in the bacterial growth in the activated sludge system resulting in a low degradation efficiency can also be caused by the strong alkalinity of the wastewater obtained in the settling tank of the flushing and wash water cycle. Such alkalinity occurs because it is conventional to inject substantial quantities of calcium hydroxide [Ca(OH).sub.2 ] into the flushing and wash water cycle to avoid bacterial growth, the latter being undesirable in this cycle. Alkalinity is so strong that pH values of up to 12 can occur.